animating weapon along with armature from character
Insted of parenting the weapon to the hand armature I would use object constrains. You constrain the Weapon to the Armature, than Blender will let you select which bone to constrain to. The nice thing about constrains is that you can keyframe their influance, so you can have the wepon copy the rotation of the hand for 30 frames but the moment you want to give it a specific rotation you can just key frame the influance at 0 and rotate it as you wish, same goes for position.

In order to have the weapon passed from one arm to another you can have 2 sets of location&amp;rotation constrains in it, one for each hand. Than as you pass it from one hand to another you keyframe the influance from one constrain to the other.
Here is a quick demo I made:https://youtu.be/Tncqr_CbkdA

Obviously you'd want to put more time into it to make the transition sooth etc.
Personally I'd not use the rotation constrains and just set the rotation of the wepon by hand but I've set it up his way since this is how it works with parenting.